Element which Generates a Magnetic Field

ABSTRACT

An element which generates a magnetic field for fastening a compressor wheel to a turboshaft of an exhaust-gas turbocharger, has a basic body and a thread. In order to specify an element which generates a magnetic field for fastening a compressor wheel to a turboshaft, which element generates as high a magnetic field strength as possible and nevertheless can absorb without damage the forces and the tightening torques which occur during fastening of the compressor wheel to the turboshaft, the entire basic body includes a magnetic material and a sleeve is arranged in the basic body, which sleeve includes a non-magnetic material and has the thread which can be screwed to a mating thread of the turboshaft.

The invention relates to an element which generates a magnetic field in order to fasten a compressor wheel to a turboshaft of an exhaust-gas turbocharger, having a basic body and a thread.

The power which is generated by an internal combustion engine depends on the air mass and the fuel quantity supplied to the internal combustion engine. In order to increase power, it is necessary to supply the internal combustion engine with an increased quantity of combustion air and fuel. The increase in power is brought about in an induction engine by increasing the cubic capacity or by increasing the rotational speed. However, increasing the cubic capacity basically gives rise to relatively heavy internal combustion engines which have relatively large dimensions and are therefore more expensive. Increasing the rotational speed entails considerable problems and disadvantages, in particular in relatively large internal combustion engines.

A technical solution which is often used for increasing the power of an internal combustion engine is supercharging. This refers to the precompression of the combustion air by means of an exhaust-gas turbocharger or else by means of a compressor which is driven mechanically by the engine. An exhaust-gas turbocharger is composed essentially of a compressor and a turbine which are connected to a common shaft and rotate at the same rotational speed. The turbine converts the energy of the exhaust gas which is usually wasted by being expelled from the exhaust pipe into rotational energy and drives the compressor. The compressor sucks fresh air in and feeds the precompressed air to the cylinders of the engine. An increased fuel quantity can be supplied to the relatively large air quantity in the cylinders, as a result of which the internal combustion engine outputs more power. The combustion process is also favorably influenced so that the internal combustion engine achieves a better overall efficiency level. Furthermore, the torque profile of an internal combustion engine which is supercharged with a turbocharger can be made extremely favorable.

As the exhaust gas quantity increases, the maximum permissible rotational speed of the combination of the turbine wheel, the compressor wheel and the turboshaft, which are also referred to as the rotating parts of the exhaust-gas turbocharger, can be exceeded. If the rotational speed of the rotating parts is exceeded to an unacceptable degree, they are destroyed, which amounts to a total write-off of the turbocharger. Particularly modern and small turbochargers with significantly smaller turbine diameters and compressor wheel diameters, which have an improved rotational acceleration behavior by virtue of a considerably smaller moment of mass inertia, are affected by the problem of the acceptable maximum rotational speed being exceeded. Depending on the design of the turbocharger, the turbocharger is completely destroyed even if the rotational speed limit is exceeded by only approximately 5%.

Very precise measurement of the rotational speed of turbochargers is carried out with an element which generates a magnetic field and which is arranged on the turboshaft and rotates along with it, in which case the magnetic field which is produced by the rotating element which generates a magnetic field is sensed by a sensor which generates an electrical signal which is proportional to the rotational speed of the turboshaft.

JP 10206447 A2 discloses a magnetized nut for fastening the compressor wheel to the turboshaft. A rod magnet, which is supported by a basic body, is arranged in this nut. In order to generate in the sensor a magnetic field which can be measured satisfactorily, on the one hand the rotating magnet must be as large as possible and must produce a sufficient field strength, and on the other hand all the magnets are formed from very brittle material so that they are not very suitable as an element for fastening the compressor wheel to the turboshaft since the brittle magnetic material can only absorb to a limited or insufficient degree the forces and tightening torques which occur when the compressor wheel is fastened to the turboshaft.

The object of the present invention is therefore to specify an element which generates a magnetic field in order to fasten a compressor wheel to a turboshaft of an exhaust gas turbocharger, which element generates a magnetic field strength which is as high as possible and nevertheless can absorb without damage the forces and tightening torques which occur when the compressor wheel is fastened to the turboshaft.

This object is achieved according to the invention by means of the features of independent claim 1.

In the entire basic body is composed of a magnetic material and a sleeve, which is composed of a nonmagnetic material and which has the thread which can be screwed to a corresponding thread on the turboshaft, is arranged in the basic body, the element which generates a magnetic field can generate a magnetic field with a high field strength, and in addition said element is suitable for absorbing without damage the forces and tightening torques which occur when the compressor wheel is fastened to the turboshaft. The element which generates the magnetic field according to the invention therefore combines two properties which are not available with a magnetic field-generating element according to the prior art.

In one refinement, the sleeve is embodied as a press-in sleeve. The press-in sleeve can be connected to the basic body very quickly and with little expenditure, which reduces costs and production time.

In a subsequent refinement, the basic body has an internal toothing system by means of which the sleeve is connected in a positively locking fashion to the basic body. As a result, the sleeve is permanently anchored in the basic body.

In one development, the sleeve is composed of a nonmagnetic metal. A sleeve composed of metal is very suitable for being pressed in to the basic body and it can absorb large forces and torques without damage. Alternatively, the sleeve is composed of a plastic. Modern plastics can also absorb large forces and torques without damage, and it is even conceivable to produce the sleeve in the basic body by using an injection molding method.

In a subsequent development, the sleeve is connected to the basic body by means of at least one crimped connection. A sleeve can easily be crimp-connected at the edges without a large degree of expenditure, as a result of which a secure and permanent connection of the sleeve to the basic body is also generated.

In a subsequent refinement, the sleeve is formed from austenitic steel. Austenitic steel is particularly strong and can therefore absorb particularly well the large forces and tightening torques which occur when the compressor wheel is fastened to the turboshaft.

Embodiments of the invention are illustrated by way of example in the figures, in which:

FIG. 1 shows an exhaust-gas turbocharger with a turbine and a compressor,

FIG. 2 shows the compressor in a sectional illustration,

FIG. 3 shows the basic body of the element which generates a magnetic field,

FIG. 4 shows the basic body which is known from FIG. 3, from a different perspective,

FIG. 5 shows a sleeve,

FIG. 6 shows the element which generates a magnetic field,

FIG. 7 shows again the element which generates a magnetic field,

FIG. 8 shows a sectional illustration of the element which generates a magnetic field, and

FIG. 9 shows the element which generates a magnetic field in order to fasten a compressor wheel to a turboshaft in its installed position in an exhaust-gas turbocharger.

FIG. 1 shows an exhaust-gas turbocharger 1 with a turbine 2 and a compressor 3. The compressor wheel 9 is rotatably mounted in the compressor 3 and is connected to the turboshaft 5. The turboshaft 5 is also rotatably mounted and is connected at its other end to the turbine wheel 4. The combination of the compressor wheel 9, turboshaft 5 and turbine wheel 4 is also referred to as the rotating parts. Hot exhaust gas is let in to the turbine 2 via the turbine inlet 7 from an internal combustion engine (not illustrated here), during which process the turbine wheel 4 is made to rotate. The stream of exhaust gas leaves the turbine 2 through the turbine outlet 8. The turbine wheel 4 is connected to the compressor wheel 9 via the turboshaft 5. The turbine 2 therefore drives the compressor 3. Air is sucked into the compressor 3 through the air inlet 16 and is then compressed in the compressor 3 and supplied to the internal combustion engine via the air outlet 6.

FIG. 2 shows the compressor 3 in a sectional illustration. The compressor wheel 9 can be seen in the compressor housing. The compressor wheel 9 is fastened on the turboshaft 5 by means of the element 17 which generates a magnetic field. The element 17 which generates a magnetic field is therefore located in the air inlet 16 of the compressor 3. The element 17 which generates a magnetic field can be embodied, for example, as a cap nut which is screwed onto a thread which is applied to the turboshaft 5 in order to clamp the compressor wheel 9 tightly against a collar of the turboshaft 5 using said cap nut.

The element 17 which generates a magnetic field in order to fasten the compressor wheel 9 to the turboshaft 5 is composed of a permanent magnet 13 which forms the basic body 11 of the element 17 which generates a magnetic field. As the turboshaft 5 rotates, the magnet 13 rotates along with it about the axis of rotation of the turboshaft 5. In the process, the magnet 13 generates a change in the magnetic field strength or the magnetic field gradient in the sensor 15. This change in the magnetic field or the field gradient generates in the sensor 15 a signal which can be processed electronically and which is proportional to the rotational speed of the turboshaft 5.

FIG. 3 shows the basic body 11 of the element 17 which generates a magnetic field. The basic body 11 of the element 17 which generates a magnetic field is formed completely from magnetic material, as a result of which a magnetic field with a high magnetic field strength emanates from the basic body 11. On the basic body 11, the north pole N and the south pole S of the magnet 13 can be seen. Furthermore, the basic body 11 has, for example, a hexagonal cap 14 on which a tool can engage. An internal toothing system 12 can be seen in the basic body 11.

FIG. 4 shows the basic body 11 which is known from FIG. 3, from a different perspective. The basic body 11 is once again formed completely from magnetic material and it can therefore generate a high magnetic field strength. The north pole N and the south pole S of the magnet 13 can be seen on the basic body 11. Furthermore, the internal toothing system 12 in the basic body 11 can also be seen clearly in FIG. 4.

FIG. 5 shows a sleeve 10 which is formed from a nonmagnetic material. This sleeve 10 can be manufactured, for example, from a high-strength austenitic steel or a plastic. Furthermore, FIG. 5 shows a crimped connection 20 on the sleeve 10.

FIG. 6 shows the element 17 which generates a magnetic field. The element 17 which generates a magnetic field is composed of the basic body 11, which was illustrated in FIGS. 3 and 4, and the sleeve 10 which is arranged therein and is known from FIG. 5. The sleeve 10 can be pressed into the basic body 11, in which case a positively locking connection of the sleeve 10 to the internal toothing system 12 of the basic body 11 is produced. The positively locking connection of the internal toothing system 12 to the sleeve 10 and the crimped connections 20 cause the sleeve 10 to be secured in a nondetachable fashion in the basic body 11. A thread 18, which can be screwed to a corresponding thread 19 on the turboshaft 5, can easily be introduced into the sleeve 10, which can be composed, for example, of high-strength austenitic steel.

FIG. 7 shows again the element 17 which generates a magnetic field, the crimped connection 20 being clearly shown here on the sleeve 10. The basic body 11 and the sleeve 20 therefore form a planar upper face which can be screwed against the compressor wheel 9.

A sectional illustration of the element 17 which generates a magnetic field is shown in FIG. 8. The basic body 11 into which the sleeve 10 is pressed can be seen again. The basic body 11 is composed of magnetic material, and the magnet 13 generates a high magnetic field strength owing to its large volume. The sleeve 10 which is made of high-strength steel is arranged in the basic body 11. The sleeve 10 is connected in a positively locking fashion to the internal toothing system 12 of the basic body 11, and in addition is permanently secured in the basic body 11 by means of the crimped connections 20. This arrangement gives the element 17 which generates a magnetic field two essential properties. On the one hand, the element 17 which generates a magnetic field produces a high magnetic field strength owing to the large volume of the magnet 13, and on the other hand the sleeve 10 with the thread 18 which is applied thereto forms a mechanically very stable component which can be used without difficulty to fasten the compressor wheel 9 to the turboshaft 5.

FIG. 9 illustrates the element 17 which generates a magnetic field in order to fasten a compressor wheel 9 to a turboshaft 5 in its installed position in the exhaust gas turbocharger 1. Firstly, the compressor wheel 9, which is fastened to the turboshaft by means of the element 17 which generates a magnetic field, can be seen. The element 17 which generates a magnetic field is composed of the basic body 11 and the sleeve 10 which is anchored therein mechanically and/or by bonding. It is to be noted in this context that the sleeve can be composed not only of a high-strength steel but also, for example, of a plastic.

The thread 8, which is screwed to the corresponding thread 19 on the turboshaft 5, can be seen in the sleeve. Here too, the basic body 11 has, for example, a hexagonal cap 14 on which a screw wrench can engage. The torques and forces which arise are transmitted completely to the sleeve 10 which is formed from high-strength material. The sleeve 10 therefore absorbs all the mechanical forces, as a result of which the compressor wheel 9 is firmly secured to the turboshaft 5. The sleeve 10 is pressed against the compressor wheel 9 by means of the crimped connection 20.

On the other hand, the large-volume magnet 13, which is a component of the element 17 which generates a magnetic field, can generate a field with a high magnetic field strength, making it possible to place the sensor 15 even at a relatively large distance from the element 17 which generates a magnetic field. The magnet 13 is, for example, capable of generating a magnetic field with a field strength which can be measured through the outer wall of the compressor housing. This has the advantage that the sensor 15 can be mounted outside the compressor housing, as a result of which it is not necessary to make an intervention into the body of the compressor housing. 

1.-7. (canceled)
 8. A fastening element that generates a magnetic field configured to fasten a compressor wheel to a turboshaft of an exhaust-gas turbocharger, the fastening element comprising: a body composed of a magnetic material, the body having a bore therethrough in a fastening direction; and a sleeve composed of non-magnetic material and having an internal thread, the sleeve being arranged in the bore of the body, wherein the internal thread of the sleeve is configured to mate with a corresponding thread on the turboshaft.
 9. The fastening element according to claim 8, wherein the sleeve is a press-in sleeve.
 10. The fastening element according to claim 8, wherein the bore further comprises an internal toothing system and the sleeve is connected in a positively locking connection in the bore of the body by the internal toothing system.
 11. The fastening element according to claim 8, wherein the sleeve is a nonmagnetic metal.
 12. The fastening element according to claim 8, wherein the sleeve is plastic.
 13. The fastening element according to claim 10, wherein the sleeve is connected to the body by at least one crimped connection.
 14. The fastening element according to claims 11, wherein the sleeve is austenitic steel.
 15. The fastening element according to claims 14, wherein the austenitic steel is a high-strength austenitic steel.
 16. The fastening element according to claim 10, wherein the sleeve is connected to the body by at a crimped connection at each end of the bore.
 17. The fastening element according to claim 10, wherein the magnetic material of the body is a permanent magnet.
 18. The fastening element according to claim 13, wherein the crimped connection forms a planar surface between the body and the sleeve.
 19. The fastening element according to claim 10, wherein the sleeve is anchored in the bore of the body by at least one of a mechanical connection or a bonding connection.
 20. The fastening element according to claim 8, wherein the body has a perimeter in a shape of a regular equilateral
 21. An exhaust-gas turbocharger comprising: a compressor comprising a compressor housing and a compressor wheel; a threaded turboshaft; a fastening element configured to attach the compressor wheel to the threaded turboshaft, the fastening element comprising: a body composed of a magnetic material, the body having a bore therethrough in a fastening direction; and a sleeve having an internal thread configured to mate with the thread on the turboshaft, the sleeve being arranged in the bore of the body; and a sensor responsive to a magnetic field generated by the fastening element.
 22. The exhaust-gas turbocharger according to claim 21, wherein the sensor is mounted to the compressor housing.
 23. The exhaust-gas turbocharger according to claim 21, wherein the sensor is responsive to the magnetic field generated by the fastening element through the compressor housing.
 24. The exhaust-gas turbocharger according to claim 21, wherein the sleeve is a non-magnetic material. 